Unbonded cloth reinforced bellows and method of manufacture

ABSTRACT

The wall of a chemically resistant bellows is formed from a loosely constructed cloth tube (preferably metallic) surrounding but not bonded to at least an inner tube of a substantially inelastic plastic material such as polytetrafluoroethylene resin. A second resin tube may be disposed over the cloth tube. Substantially nonexpandable rings are disposed externally within the valleys of the corrugations. The cloth may have a flat knit construction. The bellows can be formed by assembling the several tubes, adding the nonexpandable rings, and compressing the assembly axially in a suitable mold while the interior is filled with a medium under pressure.

United States Patent [72] Inventor Edward J. Chu

- Parsippany, NJ. 21 Appl. No. 875,789 [22] Filed Nov. 12, 1969 [45]Patented Dec. 14, 1971 [73] Assignee Resistoflex CorporationRoseland,N.J.

[54] UNBONDED CLOTH REINFORCED BELLOWS AND METHOD OF MANUFACTURE 10Claims, 5 Drawing Figs.

[52] US. Cl 138/121, 138/124 [51] Int.Cl F16| 11/00 [50] FieldofSearch138/121, 122, 124, 125, 138,153, DIG. 3

[56] References Cited UNITED STATES PATENTS 2.787.289 4/1957 Press l38/DIG 3 a f '4 "471/ O? Primary Examiner Herbert F. Ross Attorneys-Ward,McElhannon, Brooks & Fitzpatrick and Robert M. Freeman ABSTRACT: Thewall of a chemically resistant bellows is formed from a looselyconstructed cloth tube (preferably metallic) surrounding but not bondedto at least an inner tube of a substantially inelastic plastic materialsuch as polytetrafluoroethylene resin. A second resin tube may bedisposed over the cloth tube. Substantially nonexpandable rings aredisposed externally within the valleys of the corrugations. The clothmay have a flat knit construction. The bellows can be formed byassembling the several tubes, adding the nonexpandable rings, andcompressing the assembly axially in a suitable mold while the interioris filled with a medium under UNBONDED CLOTH REINFORCED BELLOWS ANDMETHOD OF MANUFACTURE The present invention relates to a chemicallyresistant bellows and to a method for fabricating same.

Chemically resistant bellows find use in expansion joints, flexiblecouplings, and the like. In particular, where such bellows have beenformed from molded polytetrafluoroethylene (P.T.F.E.) resin they havefound widespread acceptance in the chemical processing industry andelsewhere.

A number of physical characteristics determine the usefulness of aparticular bellows construction. Depending upon the particularinstallation, use may be made of one or more of the followingparameters: travel, also referred to as longitudinal movement or axialcompression and extension; misalignment, also referred to as offset orlateral deflection; and angular deflection, sometimes referred to asangular rotation. In addition, it is necessary to take into account thepressure rating or capability of the bellows structure and the effect oftemperature thereon. Finally, since the bellows is generally subjectedto movement or vibration, the flex life thereof must be considered.Unfortunately, the various parameters are often oppositely affected bychanges in construction of the bellows. Hence, any construction usuallyreflects a compromise.

Because of its chemical inertness, P.T.F.E. resin has become in certaininstances an essential material for use in a particular plumbinginstallation. Heretofore, bellows have been constructed from moldedtubes of P.T.F.E. resin reinforced with annular rings in the valleys ofthe corrugations. It is the purpose of the present invention to providea bellows structure with substantially increased pressure handlingcapability while not sacrificing flexibility, flex life, and the otherdesirable characteristics of bellows structures known heretofore. It isa further purpose of the invention to provide a P.T.F.F.. resin bellowsof greater reliability than those known heretofore.

In accordance with one aspect of the invention there is provided achemically resistant bellows comprising an annularly corrugated tubularsection characterized in that the wall of the bellows consists of afluidtight corrugated radially inner tube surrounded by a looselyconstructed fluid pervious cloth tube, the latter being maintained incontact with and conforming to the corrugated contour of the former by asubstantially nonexpandable ring member disposed in each of the valleysof the corrugated section. In a preferred embodiment the material of theinner tube is P.T.F.E. resin.

In accordance with a further aspect of the invention there is provided amethod of forming the aforesaid bellows which comprises the steps ofconcentrically interfitting at least an inner tube of a substantiallyinelastic plastic material with a surrounding tube of looselyconstructed cloth to provide a composite structure with the tubesfitting closely one within the other, installing one or moresubstantially nonexpandable rings over the composite structure, andthereafter corrugating the composite structure without causing theseveral tubes to bond one to the other and with the rings disposed inthe valleys of the corrugations.

The invention will be better understood after reading the followingdetailed description of the presently preferred embodiments thereof withreference to the appended drawings in which:

FIG. I is an elevational view in partial section showing an annularlycorrugated tubular section formed in accordance with the presentinvention;

a FIG. 2 is an enlarged view of the area within the circle 2 in FIG. 1;

FIG. 3 is a plan view showing the knitted mesh employed in the structureof FIGS. 1 and 2;

FIG. 4 is a diagrammatic view partially in section showing thearticulated mold employed in fabricating the bellows section; and

FIG. 5 is a view similar to FIG. 2 but showing a modified construction.

Throughout the figures of the drawings the same reference numerals areused to designate the same or similar parts.

Referring now to FIGS. 1, 2 and 3, there is shown a typical annularlycorrugated tubular section designated generally by the reference numeral10. The section is corrugated with a plurality of crests l1 alternatingwith valleys 12. A nonexpandable metallic ring l3 (e.g., monel metal) isdisposed in each of the valleys. For purpose of illustration, the ends14 and 15 of the corrugated section are shown cylindrical. In one modeof use, metal flanges are installed over each cylindrical end whereuponthe end is flared radially outwardly over the face of the flange toprovide a gasket face therefor.

As best seen in FIG. 2, the wall of the bellows consists of a looselyconstructed cloth tube 16 sandwiched between but not bonded to inner andouter tubes 17 and 18, respectively, of a substantially inelasticplastic material such as sintered P.T.F.E. resin.

A typical loosely constructed cloth is shown in FIG. 3 as consisting ofa knitted mesh. It is presently preferred to form such cloth fromrelatively small diameter metallic wire. In the construction of a 2-inchdiameter bellows extremely good results have been obtained with a meshknitted from 14 strands of 0.0036-inch diameter wire. The wire employedwas a type 304 stainless steel. Such cloth has a thickness ofapproximately 0.027 inch. It will be recognized that the cloth shown inFIG. 3 has a flat knit construction.

Preferably, the inner and outer tubes 17 and 18 each have an individualwall thickness of at least about one-sixteenth of an inch. In thefinished structure, substantially no clearance exists between theindividual plies. For example, employing plastic tubes having a wallthickness of 0.060 inch and a mesh having a thickness of 0.027 inch thetotal wall thickness is of the order of 0.152 inch. Allowing for usualvariations, it will be appreciated that the plies are in intimatecontact.

To provide some indication of the improved characteristics of the newbellows construction, it has been found that a 2- inch diameter bellowsconstructed in accordance with the teachings herein has a burst strengthat approximately 250 F. of about 460 p.s.i. A bellows formed fromplastic tubes of identical thickness but omitting the mesh cloth, thatis, a bellows having a wall with two plies of 0.060-inch thick plastictubing and a 2-inch diameter, had a burst strength of 280 p.s.i. underthe same conditions. Finally, a bellows with a single layer plastic wallof 0.l00 inch in thickness, all other factors remaining the same, burstat 260 p.s.i.

It is presently preferred to form the bellows described above withreference to FIGS. ll, 2, and 3, by first interfitting two tubes ofsintered extruded P.T.F.E. resin with a tube of knitted wire mesh toprovide a composite structure with the tubes fitting closely one withinthe other. This structure is then placed within an articulated mold ofthe type shown generally in FIG. 4. As seen in FIG. 4, the tubularstructure is designated by the numeral 19. The interior of the structureis filled with a pressure medium such as P.T.F.E. granules, glass beads,or a suitable hydraulic or gaseous fluid, the ends of the tubularstructure being sealed by suitable plugs, one of which is seen at 20.

End caps 21 and 22 are then slipped over the ends of the tubing andplugs after having previously located, around the intermediate portionof the structure 19, the mold rings 23, 24, and 25 which have aninternal configuration as shown in the cutaway view of the ring 23. Atthe radially inner margin there is a groove for receiving the annularreinforcing ring 12.

The lazy tong linkage 26 is pivotally joined to the end caps 21 and 22by the pins 27 and 28, respectively. In similar manner, the linkage ispivotally joined at 29 to the ring 23, at 30 to the ring 24, and at 31to the ring 25. A similar linkage is provided on the opposite side ofthe assembly although not shown in the drawings. The rings 23, M and 25should be split in any convenient manner so that upon removing suitableretaining means they may be disassembled and removed from the tubularstructure after it is corrugated.

With the tubular structure 19 mounted in the mold as shown in FIG. 4,the assembly may be placed in an oven to heat the same to the formingtemperature which may be of the order of 500 F., or thereabouts. Afterreaching temperature, the assembly may be placed between the platens ofa press and compressed longitudinally. It will be understood that thelazy tong linkage will cause the end caps and intermediate rings of themold to approach one another uniformly maintaining an equal spacingtherebetween at all times until the mold is completely closed. In theprocess, the tubular structure 19 will be deformed with the corrugationsextending radially outwardly between the adjacent rings and end caps ofthe mold. After quenching, the lazy tong linkages can be removed, alongwith the end caps and the rings 23, 24 and 25. Because of thecorrugations now in structure 19, the rings 23, 24 and 25 can be removedonly by disassembling the separate halves. ln'known manner means (notshown) should be provided for venting or adding hydraulic or gaseousfluid when such constitutes the pressure medium to maintain the pressurethereof substantially constant during the forming operation.

While the process described above is presently preferred, it may bemodified while still producing a satisfactory bellows structure. Forexample, with the interfitted tubes located in the mold and the interiorfilled with a suitable pressure medium, it is possible to compress themold longitudinally prior to the heating step thereby cold forming thematerial. With the mold restrained in its compressed condition, it isthen subjected to a heating cycle sufficient to relax the stresses setup in the plastic material during the cold forming step, whereupon it israpidly cooled or quenched. The corrugated or convoluted structure cannow be removed from the mold.

It is also contemplated that the bellows described herein may befabricated without the use of the special mold described with referenceto FIG. 4. While the lazy tong assembly serves to accurately control thelocation of the mold rings during the forming step, it is possible todispense with this arrangement. The operation becomes much morecritical, but temporary spacers can be employed to locate thereinforcing rings 13 at equally spaced intervals along the interfittedtube structure until the tube structure can be expanded radiallysufficiently to lock the rings 13 in relative axial position. Then thespacers are removed and further axial compression of the assembly cantake place with the rings 13 serving as the intermediate moldcomponents.

The specific bellows embodiment described above included an outer tubeof P.T.F.E. resin surrounding the cloth-reinforcing layer. Where thecloth layer need not be protected against the environment in which thebellows is employed, the outer P.T.F.E. tube may be eliminated as shownin FIG. 5. Thus, the structure shown in FIG. has the fluidtightcorrugated radially inner tube 17 of P.T.F.E. resin surrounded by theloosely constructed fluid pervious cloth tube 16, the latter beingmaintained in contact with and conforming to the corrugated contour ofthe former by a substantially nonexpandable ring member 13 disposed ineach of the valleys of the corrugated section. It is important that thecloth tube be continuous circumferentially and dimensioned such that thecrest portion will not expand radially so long as the valley portion isrestrained by the rings 13.

The structure shown in FIG. 5 may be formed by the same methodsdescribed above with reference to the embodiment of FIG. 2. It will beunderstood that the complete bellows may have any number of corrugationsand suitable end terminations, such as that shown in FIG. 1, for makingconnections thereto.

In the embodiments described above, the reinforcing metallic fabric wasassumed to have been formed by flat knitting. However, loosely wovenfabric might also be used satisfactorily. The cloth should be chosensuch that the burst strength of the bellows is substantially increasedwithout detracting from the flexibility and flex life of the structure.

As mentioned above, the inner and outer tubes should have a wallthickness of about at least one-sixteenth of an inch. It has been foundthat with thinner tubes the slight footprint or impression made by thewire cloth embedding in the adjacent surface of the plastic issufficient to adversely affect the ultimate rforrnance of the bellows.Particularly, where loose stran s are present, the thin walls representan extreme disadvantage since the loose wire can and will penetrate samecausing failure.

Another consideration in selecting the cloth is that it be capable ofassuming the corrugated configuration during the forming process of thebellows and that it will not adversely interfere with the attachment ofsuitable end flanges or the like.

Having described the subject invention with reference to the presentlypreferred embodiment thereof it will be understood that changes may bemade in the construction thereof without departing from the true spiritof the invention.

What is claimed is: I

1. A chemically resistant bellows comprising an annularly corrugatedtubular section characterized in that the wall of the bellows is ofmulti-ply construction with a loosely constructed cloth tube sandwichedbetween but not bonded to inner and outer tubes of a substantiallyinelastic plastic material.

2. A bellows according to claim I, wherein a substantially nonexpandablering is disposed externally of the outer tube in each of the valleys ofthe corrugated section.

3. A bellows according to claim 2, wherein said plastic material issintered polytetrafluoroethylene resin.

4. A bellows according to claim 3, wherein said cloth is formed fromrelatively small diameter metallic wire.

5. A bellows according to claim 2, wherein said cloth is formed fromrelatively small diameter metallic wire.

6. A bellows according to claim 2, wherein said inner and outer tubeseach have an individual wall thickness of at least about one-sixteenthinch.

7. A bellows according to claim 2, wherein said cloth is flat knit withmetallic strands.

8. A chemically resistant bellows comprising an annularly corrugatedtubular section characterized in that the wall of the bellows consistsof a fluidtight corrugated radially inner tube of nonmetallic materialsurrounded by a loosely constructed fluid-pervious cloth tube, thelatter being maintained in contact with and conforming to the corrugatedcontour of the former by a substantially nonexpandable ring memberdisposed externally thereof in each of the valleys of the corrugatedsection.

9. A bellows according to claim 8, wherein said cloth is flat knit withmetallic strands.

10. A bellows according to claim 9, wherein said nonmetallic material issintered polytetrafluoroethylene.

II t i l t

1. A chemically resistant bellows comprising an annularly corrugatedtubular section characterized in that the wall of the bellows is ofmulti-ply construction with a loosely constructed cloth tube sandwichedbetween but not bonded to inner and outer tubes of a substantiallyinelastic plastic material.
 2. A bellows according to claim 1, wherein asubstantially nonexpandable ring is disposed externally of the outertube in each of the valleys of the corrugated section.
 3. A bellowsaccording to claim 2, wherein said plastic material is sinteredpolytetrafluoroethylene resin.
 4. A bellows according to claim 3,wherein said cloth is formed from relatively small diameter metallicwire.
 5. A bellows according to claim 2, wherein said cloth is formedfrom relatively small diameter metallic wire.
 6. A bellows according toclaim 2, wherein said inner and outer tubes each have an individual wallthickness of at least about one-sixteenth inch.
 7. A bellows accordingto claim 2, wherein said cloth is flat knit with metallic strands.
 8. Achemically resistant bellows comprising an annularly corrugated tubularsection characterizEd in that the wall of the bellows consists of afluidtight corrugated radially inner tube of nonmetallic materialsurrounded by a loosely constructed fluid-pervious cloth tube, thelatter being maintained in contact with and conforming to the corrugatedcontour of the former by a substantially nonexpandable ring memberdisposed externally thereof in each of the valleys of the corrugatedsection.
 9. A bellows according to claim 8, wherein said cloth is flatknit with metallic strands.
 10. A bellows according to claim 9, whereinsaid nonmetallic material is sintered polytetrafluoroethylene.